The present invention relates to optical detectors and more particularly to compact optical detectors.
It is generally recognized that direct optical reading of printed matter can be faster, more efficient and more error free than keypunching data for entry into a computer. Optical reading usually involves four basic electrical functions. First, the actual optical scanning and sensing of the printed matter. Second, the analog preprocessing of the data generated by the scanning and sensing. Third, the turning of the preprocessed analog data into binary values and finally the actual recognition of the character being sensed using the binary information.
This invention deals with the first three of these electrical functions and in particular the preprocessing function of the optical reading procedure. Preprocessing is necessary because the documents being optically analyzed, no matter how elaborately they are printed, are not truly black or white. In fact the contrast difference between black and white may be as small as 15 percent and may vary from one position to another in the document. Preprocessing serves to accommodate such variations in contrast ratios. In preprocessing each element of the picture must be examined and a simple decision must be made. That decision is whether the area represented is black or white. To do this effectively the threshold for the decision can not be fixed but must constantly change to reflect the changing character of the written matter on the document. Many algorithms are known for doing this. One such algorithm continuously compares the signal from any given device of the array to the signals from adjacent devices of the sensing array and with recent histories of the maximum black and maximum white signals experienced during the optical reading. The signals from the adjacent elements and the signals representing the maximum black and maximum white encountered during sensing will unite in a specific way so that the data is not overly affected by any of the mentioned factors. To accomplish this is very difficult in a hand held optical reader because of the complexity of the algorithm being performed and the relatively low density of conventional integrated circuits that perform analog functions. This has made hand held readers in the prior art both expensive and cumbersome.